The manufacture of melt spun polymeric filaments is typically achieved by extruding a molten polymer along a melt spinning axis through shaped orifices of a spinneret and then cooling (solidifying) the filaments thus formed, usually by passing the filaments through a quench zone wherein the filaments are brought into contact with a quench gas (e.g., air). The cooled filaments are then converged and gathered at a guide (at which a suitable liquid finish may also be applied) and then delivered to a bobbin or further treatment station, for example, a draw frame.
The raw polymer is typically in the form of granules, pellets, or the like, and is usually liquefied upstream of the spin head by means of a conventional screw extruder. The molten polymer discharged from the screw extruder may then be supplied directly to the spinneret (if the screw extruder operates at sufficiently high pressure to extrude the molten polymer through the spinneret's orifices), or may first be supplied to a polymer pump which delivers the molten polymer to the spinneret under the required pressurized conditions.
As may be appreciated, when it is desired to change from one type of polymer to another so as to form a different filamentary material, it is first necessary for all of the component structures which have been wetted with the polymer to be purged (e.g., cleaned) before another polymeric filamentary material is manufactured. Otherwise, contamination would obviously result. With most low melt temperature polymers (e.g., polyesters, polyamides, etcetera), purging of the spin head may easily be accomplished on line by passing through the melt spinning machine a relatively inexpensive purge polymer (e.g., polypropylene) having a melting point below, yet sufficiently close to, the melting point of the previous filament-forming polymer processed by the machine. The purge polymer is thus processed for a time sufficient to ensure that all previously processed polymer has been removed from the system, at which time a different polymer is supplied to the machine. The machine is then operated for an additional period of time to ensure that the purge polymer is not present in the formed filaments.
On-line purging of the melt spinning machine may also be accomplished by passing a suitable polymer solvent through the spinning machine so as to dissolve any residual polymer which may be present. When the machine has been purged sufficiently, another polymer may then be processed after suitable time has elapsed to ensure that all solvent has been removed from the machine.
The on-line machine purging techniques described immediately above are not, however, usually available for high performance polymers such as, for example, polyetherketone (e.g., PEEK.TM.). The physical properties of these high performance polymers are such that they are solvent-resistant. Thus, the melt spinning machine cannot usually be solvent cleaned as is the case with lower melting point polymers. And, since the melting point of these high performance polymers is extremely elevated (e.g., in excess of about 300.degree. C.), the use of the typical polymers used to purge the machine is prohibited since the purge polymers would volatilize or have too low a viscosity at the extremely high temperatures necessary to keep the high performance polymers molten.
It has therefore been conventional practice for portions of the spinning machine which are wetted by these high performance polymers, for example, the spin head, to be physically removed from the spinning machine for cleaning and placed in a furnace so as to volatilize (i.e., burn) any residual high performance polymer. This technique, however, presents its own problems when the spin head of the spinning machine is desired to be cleaned. That is, the external heaters associated with the spin head must usually first be removed before the spin head is capable of being disassembled from the remaining melt spinning machine components. By the time the spin head is removed, therefore, the residual high performance polymer has usually cooled to an extent whereby it "freezes" the spin head to the remaining melt spinning machine components. Thus, while polymer solidification is usually not a problem with low temperature polymers (e.g., since it can be solvent-cleaned), it is a significant problem with these high performance polymers due to the physical characteristics of the latter.
What has been needed is a spin head which overcomes the above problems and which would be particularly useful in the melt spinning of high performance polymers. It is towards attaining a solution to these problems that the present invention is directed.
According to the present invention, a spin head is provided whereby the individual component parts of the head may be maintained at elevated temperatures sufficient to prevent polymer "freezing" which facilitates the disassembly of these components from the melt spinning machine so that clean components may be readily interchanged thereby minimizing machine down time. This is accomplished by providing a fixed-position (i.e., relative to the remaining components of the melt spinning machine) tubular sleeve member in which suitable electrical resistive heating elements are embedded (although external heating means could also be suitably provided). The sleeve member defines an open ended interior cavity which receives in a removable fashion, a core insert member. A conventional spinneret may therefore be removeably (e.g., threadably) coupled to the downstream end of the core insert member.
The tubular sleeve also includes a portion which bounds the polymer pump so that the latter is in opposing relationship to the screw extruder supplying molten polymer to the spin head. The core insert member therefore establishes a linear supply passageway which fluid connects the screw extruder to the pump so that the polymer is directed to the pump along an axis which is substantially perpendicular to the melt spinning axis. The pump discharges the molten polymer into a discharge passageway (which is also established by the core insert member) so as to fluid connect the polymer pump and the spinneret.
Since the core insert member, polymer pump, and spinneret are each in heat exchange relationship with the tubular sleeve, they may be maintained at elevated temperatures sufficient to prevent polymer "freezing" during disassembly. Also, since the inlet and discharge passageways are defined by the relatively monolithic core insert member, the entire spin head can be operated at conditions necessary for the melt spinning of high performance polymers (e.g., pressures up to about 10,000 psig and temperatures up to about 600.degree. C.).
Other advantages and aspects of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiment.